Staphylococcus aureus is responsible for staggering mortality and financial loss in the U.S. We have characterized a salicylate-inducible multidrug resistance mechanism in S. aureus. Salicylate-induced multidrug resistance is expressed phenotypically and involves reduced drug accumulation. Previously intrinsic multidrug resistance in S. aureus was attributed to the multidrug efflux pump NorA. We provide evidence that demonstrates that the salicylate-induced multidrug resistance mechanism is NorA-independent. We will also characterize a genotypic S. aureus multidrug resistant mechanism that results as a consequence of selection for resistance to the antimicrobial terpene mixture pinesol. This mechanism also increases resistance to the cell wall active antistaphylococcal antibiotic vancomycin. We intend to determine if the putative S. aureus multidrug efflux pump AcrB and/or the alternative transcription factor sigma B play roles in the multidrug resistance mechanisms of S. aureus being studied in our laboratories. We also plan to demonstrate that pinesol-selected multidrug resistant mutants and salicylate treated cells express altered cell wall physiology. Genes involved with pinesol-selected and salicylate-inducible multidrug resistance mechanisms of S. aureus will be identified using two procedures: Two-dimensional gel electrophoresis and a DNA subarray constructed with genes suspected to be associated with multidrug resistance in S. aureus. We hypothesize that multidrug resistance expression by S. aureus will involve a large collection of genes and gene products. We also hypothesize that the putative multidrug efflux pump AcrB and alternative transcription factor sigma B of S. aureus will play a role in the multidrug resistance expression of: i.) normal S. aureus cells; ii.) pinesol-selected mutants of S. aureus; and iii.) salicylate-induced S. aureus cells. Novel components associated with intrinsic multidrug resistance mechanisms in S. aureus might be used as targets in the development of antimicrobials used to either prevent antibiotic resistant S. aureus from arising or to halt the growth of S. aureus involved with active disease. This research will also contribute to the growing body of knowledge on the interaction of the Gram-positive coccal cells with biocides and antibiotics.